Flat no leads packages such as quad flat no leads (QFN) and dual flat no leads are connected to printed circuit boards (PCB) without the need of leads. A no leads package typically comprises several electrical I/O pads surrounding a thermal pad. They are mounted to a PCB with a pattern matching the pads of the package by applying solder paste to the pads of the package and affixing it to the PCB. Package is attached to the PCB by means of a reflow oven which melts the solder allowing the package pads to bond with electrical contacts on the PCB.
For thermal dissipation which is increasingly more important in today's integrated circuits. A central thermal pad is attached to a PCB. Improper soldering between the thermal pad and the PCB can yield hotspots which can cause the semiconductor die to overheat in places and possibly fail. Often best practices are given to the end customer as to how to best mount a no leads package to a PCB to prevent poor soldering, but are often ignored by the end customer.